1. Field of the Invention
This invention relates generally to a system for controlling a power transmitting condition of a power transmission unit mounted on a vehicle, and more particularly, to a control system for dampening a resonance resulting from a transmission of power.
The disclosure of Japanese Patent Application No. 2006-053622 filed on Feb. 28, 2006 including specification, drawings and claims is incorporated herein by reference in its entirety.
2. Related Art
An internal combustion engine such as a gasoline engine is conventionally used as a prime mover of a vehicle, and a power transmission system for transmitting a power to a driving wheel is composed mainly of a speed change mechanism. As a speed change mechanism, a geared transmission varying a speed change ratio stepwise, and a continuously variable transmission varying a speed change ratio continuously are widely known. Additionally, in recent years, an apparatus, in which a speed change ratio is substantially varied by changing a distribution rate of a power distributed from an internal combustion engine to a motor generator and to an output side through a differential mechanism, has been come into practical use. One example of apparatus of this kind is disclosed in Japanese Patent Laid-Open No. 2003-127681. According to a drive unit for hybrid vehicles suggested by Japanese Patent Laid-Open No. 2003-127681, an internal combustion engine is connected to a carrier of a planetary gear mechanism, a first motor generator is connected to a sun gear of the planetary gear mechanism, and a ring gear is connected to a member of an input side of an automatic geared transmission. The member of the input side of the automatic transmission is connected to a propeller shaft, and a second motor generator is connected to the propeller shaft. Thus, according to this drive unit for hybrid vehicles, the planetary gear mechanism functions as a distribution mechanism distributing a power of an engine to the first motor generator and to the transmission.
In case the vehicle is driven by the power of the aforementioned internal combustion engine, a revolution frequency of the internal combustion engine can be set to a value for a preferable fuel economy by using the first motor generator as a generator and controlling the speed thereof. An electric power generated by the first motor generator is fed to the second motor generator so as to operate the second motor generator as a motor. The driving force generated by the second motor generator is applied to the member of the output side, and surplus electricity is stored in an accumulator device. In case the vehicle decelerates, the second motor generator is used as a generator to regenerate energy. In case the vehicle is driven only by the electric power, the vehicle is driven by the power of the second motor generator by feeding the electric power to the second motor generator from the accumulator device. According to the apparatus suggested by Japanese Patent Laid-Open No. 2003-127681, additionally, the speed change ratio of the distribution mechanism is varied continuously by changing the revolution frequency the first motor generator, and the revolution frequency individual motor generators are varied also in case of carrying out a speed change of the geared transmission. Therefore, the electric power is exchanged among the motor generators and the accumulator device when carrying out a speed change.
On the other hand, Japanese Patent Laid-Open No. 2005-264762 discloses a power transmission unit comprising a power distribution mechanism functioning as an electrical continuous transmission, and a geared transmission mechanism functioning as a geared mechanical transmission. The apparatus suggested by Japanese Patent Laid-Open No. 2005-264762 is provided with a locking mechanism for inhibiting a differential action of the power distribution mechanism, and an engine thereof is started by rotating a motor generator connected to the power distribution mechanism and an another motor generator connected to the geared transmission mechanism in the same direction when the geared transmission mechanism is neutral.
In the apparatuses disclosed in the aforementioned documents, the internal combustion engine is employed as a prime mover so that a torque inputted from the internal combustion engine changes periodically. Moreover, no small clearance should exist in some part of the power transmission line and this causes a chattering. Further, a road surface is bumpy and not always flat, therefore, the torque inputted from a driving wheel side also fluctuates periodically. As a result, a resonance phenomenon may occur to amplify vibrations and noises.